A&P I. UNIT 6.1_ Nervous Tissue PDF

INTRODUCTION: NEW CLASS MEMBER Santiago Ramón y Cajal: -Father of modern neuroscience. -Discovered axonal growth cone. -Provided evidence for the neuron theory . -Nobel laureate Medicine 1906 (together with Camillo Golgi). © Copyright Universidad Europea. Todos los derechos reservados FUNCTIONS...

INTRODUCTION: NEW CLASS MEMBER Santiago Ramón y Cajal: -Father of modern neuroscience. -Discovered axonal growth cone. -Provided evidence for the neuron theory . -Nobel laureate Medicine 1906 (together with Camillo Golgi). © Copyright Universidad Europea. Todos los derechos reservados FUNCTIONS OF THE NERVOUS SYSTEM ✓ Sensitive: sensory or afferent neurons. ✓ Integrative: interneurons. ✓ Motor: motor or efferent neurons. Effectors: muscles-glands. © Copyright Universidad Europea. Todos los derechos reservados NEURAL COMMUNICATION SYNAPSE VERY CLOSE NEVER TOUCH © Copyright Universidad Europea. Todos los derechos reservados CELLULAR COMPONENT BY HEART NEURONS Neuroglial cells Nucleus with Nucleolus Axons or Dendrites © Copyright Universidad Europea. Todos los derechos reservados Cell body CELLULAR COMPONENT DENDRITE CAN REPLICATE WHEN BROKEN NEURONS or NERVE CELLS •The neuron is the structural and functional unit of the nervous system. •Highly specialized. •Excitable cells. •Electrical excitability: they respond to a stimulus and transform it into an action potential. •Mature mitosis. neurons do not undergo •New neurons: neural stem cells within specific regions of the brain (subventricular zone). •Degeneration and regeneration: if an axon is cut through the middle, the part that is in contact with the soma can regenerate (short distance). •Energy source: mainly glucose. © Copyright Universidad Europea. Todos los derechos reservados STRUCTURE (&FUNCTION) of NEURONS SI RETROIVE DANS FINAL JE LE TUE High capacity of protein synthesis : ribosomes, RER. = SOMA Receptor part Integrative part Conducting part Principles of Human Anatomy and Physiology, 11e © Copyright Universidad Europea. Todos los derechos reservados 15 NEURONS DENDRITES Functions: ▪ Specialized processes for the reception of signals (membrane receptors). Structure: DENDRITE: RECEPTOR (R DE DENDRITE CELL BODY Image of a Purkinje cell by Ramón y Cajal. Public domain. © Copyright Universidad Europea. Todos los derechos reservados - Highly branched often covered by projections called “dendritic spines”. - Dendron: “tree”. - Cytoplasm: Nissl bodies (RER), mitochondria. NEURONS CELL BODY or SOMA INTEGRATIVE Functions: nutrition and metabolism. receptor of signals. Structure: - Single nucleus with prominent nucleolus. - Cytoplasm: Nissl bodies (RER), lysosomes, mitochondria, Golgi apparatus, synaptic vesicles. NOT TO LEARN - Cytoskeleton (microtubules, intermediate filaments or neurofibrils). © Copyright Universidad Europea. Todos los derechos reservados NEURONS THE AXON Functions: ▪ propagation of signals (nerve impulses) Structure: © Copyright Universidad Europea. Todos los derechos reservados - Long, thin & cylindrical projection. - Cytoplasm=AXOPLASM: mitochondria, microtubules and neurofibrils. No protein synthesis. - Cell membrane = AXOLEMMA. - AXON HILLOCK (cone-shaped region where axon binds to soma) (AH). - Initial segment (closest to axon hillock) (IS). - Trigger zone (junction between AH and IS). - Axon collaterals (side branches). - Axon terminals = TELODENDRIA (with synaptic vesicles filled with neurotransmitters). - Synaptic end bulbs. - Varicosities. NEURONS THE AXON: SYNAPSE Synapse or neuronal junction is the site of communication between a neuron and its effector. Axo-somatic Axo-dendritic Axo-axonic Neurotransmitter is the chemical released at the synapse. "You are your synapses. They are who you are." Joseph LeDoux, 2002 (in Synaptic Self) © Copyright Universidad Europea. Todos los derechos reservados David Goodsell. The Scripps research Institute. NEURONS THE AXON: AXONAL TRANSPORT The cell body or soma is the place where most protein synthesis occurs. ▪ Neurotransmitters & repair proteins need to be transported along the axon. – – © Copyright Universidad Europea. Todos los derechos reservados Slow axonal flow • ANTEROGRADE flow: away from cell body. • Movement at 0,2-4 mm per day (cytosolic proteins). Fast axonal flow • Moves materials along the surface of microtubules (uses ATP). • 200-400 mm per day (cargoes vesicles). • Transports in both directions: • Anterograde: soma axon terminal. • Retrograde: axon terminal soma. NEURONS FAST AXONAL TRANSPORT Kinesin Anterograde transport SYNAPTIC VESICLES, MITOCHONDRIA Synaptic vesicles recycled Dynein Retrograde transport TROPHIC FACTORS, MITOCHONDRIA, VESICLES FOR RECLYCLING © Copyright Universidad Europea. Todos los derechos reservados TYPES OF NEURONS According to their structure (number of processes) According to their function © Copyright Universidad Europea. Todos los derechos reservados Unipolar Bipolar Multipolar Sensory Interneurons Motor TYPES OF NEURONS STRUCTURAL CLASSIFICATION (number of processes – neurites) Several dendrites and 1 axon CNS. Motor neurons. © Copyright Universidad Europea. Todos los derechos reservados Two neurites (1 main dendrite and 1 axon) Retina, inner ear, brain olfactory area. 1 process (NEURITE) only. Sensory receptors. Soma within ganglia. TYPES of NEURONS According to their function •Sensory or afferent neurons: – Receive signals from the external environment or from skin, muscles, joints, sense organs & viscera. – Transmit signals towards the CNS. – Receptor function. •Interneurons (association neurons): – Connect sensory neurons to motor neurons. – CNS. 90% of neurons in the body. – Integrative or associative function. •Motor or efferent neurons. – Send signals from the integration or control centre to the effector (muscles and glands) through cranial or spinal nerves. – Conducting function. © Copyright Universidad Europea. Todos los derechos reservados SUMMARY INFOGRAPHICS NEURON HISTOLOGY © Copyright Universidad Europea. Todos los derechos reservados OTHER NEURONS Shape, researcher who described them… © Copyright Universidad Europea. Todos los derechos reservados NEUROGLIA MATURE NEURONS CANT DIVIDE • Smaller than neurons. • 25 times more numerous. • Do not propagate action potentials. • Can divide. © Copyright Universidad Europea. Todos los derechos reservados BY NEUROGLIA Central nervous system: ASTROCYTES •Star-shaped cells. •Fibrous astrocytes (white matter) and protoplasmic astrocytes (gray matter). Functions: •Part of blood-brain barrier by covering blood capillaries. Astrocytes in culture. GFAP staining •Provide structural support. •Protect neurons (toxic blood products). •Metabolize neurotransmitters. •Regulate chemical environment Ca2+, K+ balance. •Memory and learning (synapses). Pia matter •Secretory: chemical substances that regulate growth and cellular migration during development. © Copyright Universidad Europea. Todos los derechos reservados NEUROGLIA ASTROCYTES In recent years an important role in modulating the synapse has been discovered. Tripartite synapses. © Copyright Universidad Europea. Todos los derechos reservados Mente y cerebro A. Araque y M. Navarrete. 2013 NEUROGLIA ASTROCYTES AND BLOOD BRAIN BARRIER (BBB) • The brain requires 10 times more O2 and nutrients than other organs, so it requires high vascularization. • Glial cells have a very Neuron Oligodendrocyte important role in this vascularization, during the development of the CNS. Axon Presynaptic element Postsynaptic element • Animal models in which the regeneration of these glial cells is diminished, their vascularization density is altered. © Copyright Universidad Europea. Todos los derechos reservados Microglia Blood vessel Astrocyte NEUROSCIENCE: GLIA—MORE THAN JUST BRAIN GLUE». NICOLA J. ALLEN & BEN A. BARRES, NATURE, VOL. 457, FEBRUARY 2009 NEUROGLIA Central nervous system: OLIGODENDROCYTES Most common glial cell type. Involved in myelination: they form and maintain myelin sheath around axons in CNS. Myelin layer: multilayered covering made of lipids and proteins that isolates axons and increases the speed of the conduction of the nerve impulse. Analogous to Schwann cells of PNS. © Copyright Universidad Europea. Todos los derechos reservados NEUROGLIA Central nervous system: MICROGLIA Derived from cells of the immune system (mesoderm). Small cells with few projections found near blood vessels. WHEN ⋲ BACTERIA Resting and activated cells. Cytotoxic (ROS): release substances that cause death of bacteria or viruses. Phagocytic role – they clear cells/bacteria/biological debris. © Copyright Universidad Europea. Todos los derechos reservados away dead EPENDYMAL CELLS Central nervous system: EPENDYMAL CELLS •Epithelial cells. Simple cuboidal to columnar epithelium with microvilli and cilia = EPENDYMA. •Produce, monitor, and contribute to circulation of cerebrospinal fluid (CSF). •Structural function: form epithelial lining of the brain ventricles & central canal of the spinal cord. Leaky barrier between CSF and IF. •They form the epithelial layer of the choroid plexus in contact with blood vessels. Impermeable barrier. •They can acquire neural stem cell properties. © Copyright Universidad Europea. Todos los derechos reservados NEUROGLIA Peripheral nervous system: SATELLITE CELLS Flat cells surrounding peripheral ganglia. neuronal cell bodies in Functions: Support neurons in the PNS ganglia. Participate in signaling processing and transmission in sensory ganglia. Regulate exchange of substances between soma and interstitial fluid. © Copyright Universidad Europea. Todos los derechos reservados NEUROGLIA Peripheral nervous system: SCHWANN CELLS BY Non specific shaped cells. Functions: Axon myelination in the PNS. Each Schwann cell surrounds (“tape like wrapping”) only 1 axon in the PNS. Regeneration: main reason why PNS neurons regenerate better than CNS ones. Non myelinating Schwann cell: a single cell can enclose many unmyelinated axons. © Copyright Universidad Europea. Todos los derechos reservados Theodor Schwann (19th century) MYELIN SHEATH Multi-layered lipid and protein covering that electrically insulates axons and increases the speed of nerve impulse. CNS Oligodendrocytes PNS Schwann Cells One cell myelinates parts of several axons One cell covers 1 mm length of ONE axon No axonal regeneration: no neurolemma Neurolemma = axonal regeneration Fetal development © Copyright Universidad Europea. Todos los derechos reservados GREY AND WHITE MATTER = DENDRITE White matter = myelinated processes (white in color). = CELL BODY Gray matter = neuron’s cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (darker – grey- color). ▪ In the spinal cord = gray matter forms an H-shaped inner core surrounded by white matter. ▪ In the brain = a thin outer shell of gray matter covers the surface & it is also found in clusters called nuclei inside the CNS. © Copyright Universidad Europea. Todos los derechos reservados NEURONAL CELL BODIES form clusters Within the PNS = Ganglion (ganglia) Within the CNS = Nucleus (nuclei) © Copyright Universidad Europea. Todos los derechos reservados AXONS form BUNDLES Within the PNS = NERVES CRANIAL SPINAL Within the CNS = TRACTS DTI (diffusion tensor imaging) image of the brain. Taken from http://houseofmind.tumblr.com/post/1103019108/picture-of-thebrain-taken-using-dti-dti-stands © Copyright Universidad Europea. Todos los derechos reservados MAIN STRUCTURES of the PNS A nerve is a bundle of hundreds or thousands of axons, each of which courses along a defined path and serves a specific region of the body. 12 pairs of cranial nerves emerge from the base of the brain through foramina of the skull. 31 pairs of spinal nerves emerge from the spinal cord, each serving a specific region of the body. Ganglia, located outside the brain and spinal cord, are small masses of nervous tissue, containing primarily cell bodies of neurons. Enteric plexuses or “brain of the gut”. Sensory receptors are either parts of neurons or specialized cells that monitor changes in the internal or external environment. © Copyright Universidad Europea. Todos los derechos reservados CLINICAL CONNECTION_ DENTISTRY © Copyright Universidad Europea. Todos los derechos reservados